The present invention relates to a power transmission mechanism provided between a drive source and a driven machine. More specifically, this invention relates to a power transmission mechanism that interrupts transmission between a drive source and a driven machine when an excess load torque is produced by the driven machine.
In general, a power transmission mechanism is provided between a drive source, such as an engine or a motor, and a driven machine, such as a compressor. When an abnormality (e.g., seizure) occurs in the driven machine, the power transmission mechanism positively shuts off power transmission between the drive source and the driven machine to prevent the excess load torque from affecting the drive source.
For example, Japanese Unexamined Patent Publication (KOKAI) Hei No. 8-319945 discloses a clutchless compressor in which a pulley, which is fitted over the end portion of the rotary shaft, is driven by an engine. The pulley, or power transmission mechanism, has a plurality of arcuate holes arranged at predetermined intervals on an imaginary circle about the axis of the rotary shaft. The portions between adjacent pairs of holes form break portions. When the rotary shaft is unable to rotate due to an abnormality in the internal mechanism of the compressor and a load torque equal to or greater than a predetermined value acts on the break portion, the break portion breaks. Consequently, the power transmission to the rotary shaft from the engine is cut off.
According to the power transmission mechanism of the aforementioned publication, the break portion does not always fully break when the load torque reaches the predetermined value. Specifically, for example, the failure stresses of the individual members, if they are of the same kind or are the same member, are not quite the same and have a certain variation. It is therefore actually very hard to reliably break the break portion in the vicinity of a load torque where breaking is expected in individual power transmission mechanisms that have such individual differences. Accordingly, a simple structure that has a break portion merely provided at a part of the pulley is not practical, and there is no guarantee that breakage will occur as expected.
It is therefore an object of the present invention to provide a power transmission mechanism that reliably breaks in the vicinity of a desired load torque to accomplish suitable power cutoff.
To achieve the above object, this invention provides a power transmission mechanism for coupling a drive source to a driven machine in an interruptible manner. The power transmission mechanism includes a first rotary body, which rotates in synchronism with the drive source, and a second rotary body, which rotates in synchronism with the driven machine. Coupling means couples the first rotary body and the second rotary body in a synchronously rotatable manner. Engagement means engages with the coupling means when the load torque of the driven machine exceeds a predetermined value. The engagement means, which is in engagement with the coupling means, increases stress at a specific portion of the coupling means to break the coupling means.
A power transmission mechanism provided according to another aspect of this invention includes a first rotary body, which rotates in synchronism with the drive source, and a second rotary body, which rotates in synchronism with the driven machine. Coupling means couples the first rotary body and the second rotary body in a synchronously rotatable manner. As the load torque of the driven machine increases, the stress of the coupling means increases. Engagement means engages with the coupling means to increase the ratio of the change in the stress of the coupling means to the change in the load torque of the driven machine. The engagement means engages with the coupling means to break the coupling means when the load torque of the driven machine exceeds a predetermined value.